CASE 11063 Published on 27.06.2013

Patellar tophaceous gout involving the quadriceps femoris tendon

Section

Musculoskeletal system

Case Type

Clinical Cases

Authors

Leonardo Giarraputo1, Sergio Savastano1, Stefano Santini2, Alberto Momoli2, Stefano Trupiani1, Luca Boi1

U.O. Radiologia1 and U.O. Ortopedia2 - Ospedale San Bortolo - V.le F. Rodolfi 37 36100 Vicenza, Italy
Patient

81 years, male

Categories
Area of Interest Musculoskeletal joint ; Imaging Technique Conventional radiography, MR
Clinical History
The patient complained of a painful long-lasting suprapatellar mass of the right knee causing movement impairment; he was non-responder to anti-inflammatory therapy. History and physical examination were otherwise negative. Preoperative routine blood chemistry evidenced a high serum urate concentration (11.3 mg/dL; upper normal limits 8 mg/dL).
Imaging Findings
Plain radiography of the knee showed a focal osteolysis with sclerotic margins of the upper pole of the patella, swelling of the suprapatellar soft tissue and irregular calcifications at the insertion of the femoral quadriceps tendon (Fig. 1a, b). On MRI the femoral quadriceps tendon was thickened, inhomogeneous and encompassed by a fusiform tissue swelling eroding the upper pole of the patella. The peritendon swelling showed an intermediate signal on T1W-MR (Fig. 2a). On T2W-FS-MRI the lesion was hypointense but inhomogeneous because of small hyperintense foci more conspicuous in the lytic lesion of the patella (Fig. 2b, c). No other remarkable findings were evident. Surgical toilette and tenorrhaphy of the femoral quadriceps tendon were performed.
Discussion
Tophaceous gout is the chronic manifestation of sodium urate microcrystals precipitation in the articular cartilage, subchondral bone, synovial membrane, capsular tissues and tendons; clinical presentations include monarticular or polyarticular arthritis [1, 2]. Cutaneous and subcutaneous tophi are typical of an advanced disease and are usually associated with an articular involvement [2]. Recurrent gout attacks, hyperuricaemia, evidence of subcutaneous tophi, periarticular or intra-articular masses with marginal osteolysis make the diagnosis easy to achieve, but lack of these criteria can cause a radiological misdiagnosis [2]. Pathogenesis of bone erosion remains unclear; possible explanations comprise a mechanical pressure from tophi, developing of erosive synovitis caused by urate crystals, production of enzymes digesting cartilage and osseous matrix, osteoclast activation within the tophus [2-7].
Radiologically findings of chronic gout are appreciable after many years from the onset of the disease and include soft-tissue or intraosseous mass, non-demineralising erosive arthropathy with sclerotic or overhanging margins [2, 3, 8]. Advanced features are articular space involvement, periosteal new bone formation, extra-articular erosions, intraosseous calcification, joint space widening and subchondral collapse.
CT can easily depict tophi, which a typical density of 160-170 HU, and their relationship with bone erosion. Preliminary reports suggest high sensitivity of dual energy CT in detecting of tophi, also in the preclinical phase [9, 10].
Because its intrinsic capability in tissue characterisation MRI is the procedure of choice to identify bone, articular and soft tissue tophi. However these findings are not specific since tophi show a broad spectrum of signal intensity depending on arrangement and variable contribution of protinaceous material, fibrous tissue, microcrystals and haemosiderin [2, 11, 12]. Tophi are usually isointense to muscles on T1W-MRI and a heterogeneous intermediate to low signal on T2W-MRI, relying on inflammatory and/or oedematous components [2, 7, 11]; a peripheral or inhomogeneous enhancement of tophi can be appreciated after gadolinium administration [2, 11, 12]. Tophaceous gout can involve all the components of the knee but with some preferential localisations: the Hoffa pad, the anterior articular recess, the intercondylar notch, the intercondylar roof and the popliteal groove [2, 7, 11]; in most of cases erosion of adjacent bones coexists [2].
MRI is not indicated in patients with a clinically and radiologically typical disease; nevertheless, because of a possible atypical presentation, the radiologist should consider the diagnosis of tophaceous gout if a heterogeneous low or intermediate periarticular mass eroding the adjacent bone is detected on T2W-MRI [13].
Differential Diagnosis List
Patellar tophaceous gout involving the quadriceps femoris tendon
Septic arthritis
Chondroblastoma
Giant cell tumour
Chondrosarcoma
Pigmented villo-nodular synovitis
Synovial osteochondromatosis
Amyloid arthropathy
Final Diagnosis
Patellar tophaceous gout involving the quadriceps femoris tendon
Case information
URL: https://www.eurorad.org/case/11063
DOI: 10.1594/EURORAD/CASE.11063
ISSN: 1563-4086

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